The present development is described with primary reference to servo motors, but is applicable to other types of motors. Accordingly, it is not intended that the present development be limited to servo motors unless specified as such.
Rotary servo motors and other motors are widely known and used to provide rotary motion control for industrial machinery and other applications. A rotor rotates relative to a stator in response to control input commands from a motor drive. An output shaft of the servo motor is operably connected to the rotor to rotate therewith. The output shaft projects outwardly from or is otherwise accessible at the motor housing at a front end. A position and/or speed feedback device, often referred to as an “encoder,” is operatively associated with the output shaft of the motor at an opposite rear end of the motor housing and provides feedback to the motor drive as to the angular position of the output shaft and rotor such that rotation of the output shaft is further controlled in response to the feedback to obtain a precise desired angular position for the rotor and output shaft connected thereto. Servo motors often further include a holding brake that is selectively applied after the rotor is stopped in the desired angular position to hold the output shaft and rotor in such desired angular position and/or a motor can include a stopping brake used to stop rotation of the rotor and components connected thereto.
FIG. 1 shows such a conventional servo motor M′ comprising a housing H′ with a front wall FW′, a rear wall RW′, and a side wall SW′ that can be rectangular, cylindrical or otherwise shaped in cross-section and that extends axially between and interconnects the front wall FW′ and rear wall RW′. Between the front wall FW′, rear wall RW′ and side wall SW′, the housing defines a hollow interior space SP′ in which a stator ST′ is supported. A rotor RT′ is rotationally supported inside the stator ST′, and the rotor RT′ is operably coupled to an output shaft OS′ such that the output shaft OS′ rotates directly or indirectly with the rotor RT′ when the motor is energized. The output shaft OS′ extends axially or longitudinally in the motor housing H′ along a longitudinal axis X′ and is rotationally supported by a front bearing FB′ located adjacent the front wall FW′ and a rear bearing RB′ that is spaced inwardly or rearwardly toward the rear wall RW′ with respect to the front bearing FB′. The front bearing FB′ is typically located in a front end cap. The output shaft OS′ extends outside of the housing space SP′ through the front wall FW′ of the motor housing H′ and is adapted to be operably coupled to an associated machine or other structure to be rotated by the output shaft OS′. The motor housing H′ extends axially or longitudinally along the longitudinal axis X′ of the output shaft OS′, and the motor housing H′ includes a mid-point MP′ located halfway between the front wall FW′ and rear wall RW′ along the longitudinal axis X′.
The motor housing H′ includes a front end FE′ adjacent the front wall FW′ and includes a front region FR′ that extends between the front wall FW′ and the housing midpoint MP′. Similarly, the motor housing H′ includes a rear end RE′ adjacent the rear wall RW′ and includes a rear region RR′ that extends between the rear wall RW′ and the housing midpoint MP′. The motor housing H′ includes one or more mounting flanges MF′ or other mounting structures located adjacent the front end FE′ including apertures defined therein for receiving respective fasteners for securing the housing to an associated machine or other support T′ for use of the motor M′. In certain installations, as shown in FIG. 1, the rear end RE′ of the motor housing H′ is unsupported by an associated mounting structure such that the rear end RE′ and rear region RR′ of the housing are cantilevered relative to the front end FE′ of the housing.
The output shaft OS′, which can comprises a single shaft or multiple interconnected shaft portions, is rotationally supported in the interior space SP′ of the motor housing H′ by a front bearing FB′ located in the front region FR′ of the housing H′ and by a rear bearing RB′ located in the rear region RR′ of the housing. The motor M′ further comprises a position and/or speed feedback device such as an encoder E′ located in the housing rear region RR′ and operatively associated with the output shaft OS′. The encoder E′ senses or detects the angular position of the output shaft OS′ as the output shaft rotates about the axis X′. The motor M′ comprises an electrical power and data connector C′ for communicating power to the windings of the stator and for communicating data between the encoder E′ and an associated motor drive system through one or more associated cables, such as a single cable that includes multiple separate conductors for powering the windings of the motor, for controlling the brake assembly BA′, and for carrying feedback data and temperature data. The connector C′ can be provided as part of a removable cap that covers the encoder E′. A wall (not shown) separates the encoder E′ from the rear bearing RB′. In one example, a rear end cap is connected to the housing H′ and holds the rear bearing RB′ on an inner side and holds the encoder or other feedback device E′ on the opposite outer side.
The motor M′ further comprises a brake or brake assembly BA′ for selectively braking or holding the output shaft OS′ so that the output shaft OS′ is prevented from rotating and held in a fixed angular position when the brake assembly BA′ is engaged. The brake assembly BA′ is located in the housing rear region RR′ near the rear bearing RB′ and encoder E′, and can be fixedly secured to a rear end cap. The location of the brake assembly BA′ in the rear region RR′ of the motor housing H′ has been deemed to be suboptimal in certain instances because the brake assembly BA′ generates significant heat and brake dust that can degrade the performance and lifespan of the encoder E′. Also, the mass of the brake assembly BA′ located in the cantilevered rear region RR′ of the motor housing H′ can lead to increased vibrations in the output shaft OS′ and motor M′ overall.
In a typical arrangement, as shown in FIG. 2, the brake or brake assembly BA′ comprises a brake housing 10′ that secured to the motor housing H′ in the space SP′ by one or more fasteners. The brake housing 10′ includes a base 12′ and a backing plate 14′ that is secured to the base 12′ by a plurality of fasteners 14f′ (only one fastener 14f′ is shown in FIG. 2) such that the backing plate 14′ is axially spaced from the base 12′. Both the base 12′ and backing plate 14′ annular in general structure, and the motor output shaft OS′ extends coaxially through both the brake assembly base 12′ and backing plate 14′. A brake hub 20′ is keyed, splined, or otherwise connected to the motor output shaft OS′ to rotate therewith, or the hub 20′ is integrally provided as part of the output shaft OS′.
The brake assembly BA′ further comprises a movable armature 30′, typically an annular plate structure that is coaxially located about the hub 20′ and output shaft OS′, but that is axially movable along the longitudinal axis X′ of the output shaft OS′.
The brake assembly BA′ also includes one or more springs 36′ operably positioned in the base 12′ that operate between the base 12′ and the armature 30′ to continuously bias and urge the armature 30′ toward its engaged position, away from the base 12′ and toward the backing plate 14′. The spring(s) 36′ can comprise a plurality of axially extending coil springs arranged circumferentially about the base 12′ or can comprise another spring arrangement such as, e.g., a disc spring coaxially positioned about the output shaft OS′ between the base 12′ and the armature 30′. Alternatively, the brake assembly BA′ can be a permanent magnet brake assembly in which the spring(s) 36′ is replaced by one or more permanent magnets that urge the armature 30′ into its engaged position.
An annular brake rotor 40′ is engaged with the hub 20′. In particular, the rotor 40′ comprises an inner or hub portion 42′ that is keyed, splined, or otherwise operably coupled to the hub 20′ to rotate with the hub 20′ and slide axially relative to the hub 20′ such that the brake rotor 40′ is axially slidable or movable relative to the hub 20′ along the longitudinal axis X′. The rotor 40′ is positioned axially between the armature 30′ on one side and the backing plate 14′ on the other opposite side. Typically, a friction material is included on one or both opposite faces of the rotor 40′ and/or on the faces of the armature 30′ and/or backing plate 14′ that are oriented toward the rotor 40′ such that when the rotor 40′ is urged by the armature 30′ into abutment with the backing plate 14′ and the armature 30′ clamps the rotor 40′ into abutment with the backing plate 14′, the rotor 40′ is prevented from rotating about the axis X′ which prevents the hub 20′ and output shaft OS′ from rotating about the longitudinal axis X′.
The brake assembly BA′ is normally engaged or in its “on” configuration because armature 30′ is normally spring-biased by the biasing spring(s) 36′ toward and into an engaged position where the armature 30′ firmly urges the brake rotor 40′ into engagement with the backing plate 14′ such that the rotor 40′ is tightly captured or sandwiched between the armature 30′ and the backing plate 14′ (together with the friction material) and such that the rotor 40′ is restrained against rotation about the longitudinal axis X′ of the output shaft OS′. When the rotor 40′ is restrained against rotation, the output shaft OS′, itself, is also restrained and prevented from rotating about the longitudinal axis X′.
To release or disengage the brake assembly BA′ so that it is in its “off” configuration, the brake assembly BA′ further includes at least one electromagnetic coil 50′ located in the brake housing base 12′. The coil 50′ is selectively energized by the associated motor drive system connected to the motor M′ to establish an electromagnetic force about the coil 50′. Because the armature 30′ comprises a magnetic metal or other magnetic material, when the coil 50′ is energized, the electromagnetic force of the coil 50′ draws the armature 30′ toward its disengaged position, i.e., toward the brake housing base 12′ away from the brake rotor 40′ and backing plate 14′, into a disengaged or released position against the biasing force of the spring(s) 36′ (or against the biasing force of the permanent magnets if used in place of the spring(s) 36′). When the armature 30′ is moved into its disengaged position and held in its disengaged position by the electromagnetic force of the coil 50′, the brake rotor 40′ is released and disengaged from the armature 30′ and backing plate 14′ and the rotor 40′ slides axially away from the backing plate 14′ sufficiently to allow the rotor 40′ to rotate about the longitudinal axis X′, along with the hub 20′ and output shaft OS′ of the motor M′.
When the brake assembly BA′ is a holding or parking brake, the brake assembly BA′ is not engaged until the output shaft OS′ has stopped rotating or at least substantially stopped rotating, i.e., the brake assembly BA′ is typically not used to stop a rotating rotor 40′. The brake assembly BA′ is also typically released before the motor M′ is again energized to rotate the output shaft OS′ so that the brake BA′ is never in its engaged or “on” while the output shaft OS′ is being rotationally driven. In some cases, the brake assembly BA′ acts as a stopping brake that slows and stops the rotor 40′ when the brake assembly BA′ is engaged.
Motor brakes as described above have heretofore been associated with certain drawbacks. As noted, known brake assemblies BA′ are mounted in the rear region RR′ of the motor M′ near the encoder E′. In some applications, the motor M′ is mounted to an the associated support structure by a mounting flange MF′ or the like that is located at the front end FE′ of the motor, and the opposite rear end RE′ of the motor is unsupported and cantilevered outwardly relative to the front end FE′. In such case, the significant cantilevered mass of the brake assembly BA′ can sometimes lead to undesired vibration or misalignment of the output shaft OS′ during use of the motor M′, both of which can lead to operational drawbacks and can increase wear and degrade motor performance and operational life.
Also, a motor brake BA′ as described generates significant heat due to the need to energize the brake coil 50′ repeatedly to release the brake assembly BA′ and to hold the brake assembly BA′ in its released position during rotation of the output shaft OS′. Known servo motor brake designs and locations lead to such heat being transmitted to the encoder E′, which can degrade performance and lifespan of the encoder E′. Furthermore, such known designs are suboptimal in terms of brake cooling and capture too much heat in the motor housing H′. Also, locating the brake assembly BA′ adjacent the encoder E′ can cause brake dust to contaminate the encoder which can reduce its life, increase heat, and reduce its lifespan and performance.
In addition, the motor brake assembly BA′ and other known designs do not provide desired feedback or diagnostic information about the health and performance of the brake BA′, itself, such as brake release, brake dragging, and shorts in the brake coil. As such, an unexpected brake failure can cause an unscheduled malfunction of the motor M′, which is highly undesired in applications such as manufacturing, entertainment, transportation, and the like.
Accordingly, it has been deemed important to provide a motor brake system that increases safety of people in fields such as entertainment, manufacturing, and the like through advanced diagnostic monitoring, preventing unexpected failures, improved protection, higher utilization and increased availability of assets. This is especially important for applications where gravity assisted and vertically hanging loads are present, such as in entertainment or in industrial automation applications for packaging, converting, robotics, machine tooling, conveyors, cranes, etc. A need has been identified for improving safety integrity of brake control (improved Safety Integrity Level (SIL) rating), reducing vibration and improving thermal performance of servo motors and other motors. The present development as described below provides the above-noted benefits and advantages and others while providing better overall results. As such, a motor brake must function properly over the life of the motor, and any performance degradation of the motor brake must be identified early to ensure that the motor brake can be monitored and repaired if necessary.